One of the overall goals of this project is an increased understanding of structure-activity relationships for malignant cell-specific cationic photosensitizers (CPS) and the intracellular mechanisms for their actions. The second goal is to use the mechanistic information derived from this and the other Projects to increase the efficacy of photochemotherapy (PCT) by using multiple sensitizers with different actions or by inhibiting glycolysis. The specific aims are: 1. To synthesize new CPS and define their structure-activity relationships and mechanisms of phototoxicity in vitro and in vivo. a. Starting from our current knowledge, we will prepare CPS in the oxazine/thiazine, triarylmethane and kryptocyanine classes. b. Efficacy, selectivity and oxygen-dependence will be characterized on malignant and non-malignant cells, and dark toxicity and clearance determined in vivo. c. Selected CPS will be characterized in vivo, measuring pharmacodynamics and examining dose-response surfaces for tumors and normal skin. Percent of tumor kill, regrowth kinetics and long term cures will be determined under conditions which maximally spare normal tissues. d. Sites of dye accumulation and in vivo sites and mechanisms of photodamage will be determined for selected CPS. Intracellular sites and mechanisms of dark- and phototoxicity will be defined, and this information will be used in the studies of multiagent and combination PCT. e. In vivo and in vitro data will be correlated with CPS structures to guide further synthesis. 2. To investigate the use of multiagent PCT, employing cationic or anionic PS which target different intracellular or tissue sites, or which act by different photochemical mechanisms (e.g. oxygen-independent and oxygen- dependent). 3. To examine the use of combination PCT, employing agents such as lonidamine which interfere with glycolysis and should potentiate the effects of light-induced damage to blood vessels or to mitochondria.